Nelson-Barr ultralight dark matter

TL;DR

This paper proposes a Nelson-Barr model where a naturally light scalar acts as dark matter, leading to unique phenomenology and testable predictions via quantum sensors like nuclear clocks.

Contribution

It introduces a new light scalar dark matter candidate within the Nelson-Barr framework, distinct from the QCD axion, with potential for experimental detection.

Findings

The scalar causes CKM elements to vary periodically in time.

The model predicts observable effects in quantum sensors such as nuclear clocks.

It offers a novel approach to test dark matter and CP-violation physics.

Abstract

We show that, in the Nelson-Barr solution to the strong CP-problem, a naturally light scalar can arise. It gives rise to a completely new phenomenology beyond that of the celebrated QCD axion, if this field constitutes dark matter, as the CKM elements vary periodically in time. We also discuss how the model can be tested using quantum sensors, in particular using nuclear clocks, which leads to an interesting synergy between different frontiers of physics.